The present invention relates to generators of electric energy based on the thermoelectric effect. In particular, the invention regards a generator of electric energy of the type comprising:
a layer of thermoelectric material; and
means for guiding a first flow of fluid at a higher temperature and a second flow of fluid at a lower temperature in a direction parallel and adjacent to the two opposite sides of the layer of thermoelectric material,
in such a way as to produce a heat transfer through said layer of thermoelectric material, from the side adjacent to the flow of fluid at a higher temperature to the side adjacent to the flow of fluid at a lower temperature
so as to generate a difference of electrical potential between two electrical terminals in electrical connection with the two opposite sides of the layer of thermoelectric material.
In the present description and in the attached claims, the expression “layer of thermoelectric material” is understood as referring both to the case of one or more pairs of elements made of thermoelectric material and to the case of a distribution of a number of thermoelectric cells, which include in themselves, in addition to the thermoelectric material, also the corresponding electrical-connection contacts, as will be illustrated in greater detail in what follows.
The problem of exploiting in an efficient way a difference in temperature between two flows of fluid in order to produce electric energy by means of the thermoelectric effect has already been tackled in the past, without being solved in a satisfactory way. The main difficulty consists in obtaining an acceptable efficiency of the process of energy generation. This can be explained with reference to the diagram illustrated in FIG. 1. In said figure, the reference number 1 designates a layer of thermoelectric material having two opposite sides H, C, lapped, respectively, by a flow of hot fluid F1 and by a flow of cold fluid F2, which have opposite directions with respect to one another. In order to obtain the maximum efficiency of operation of the layer of thermoelectric material 1, the ideal situation would be the one represented by the temperature diagram designated by Ti. According to said ideal situation, the temperature of each of the two fluids remains constant for points within the flow that are set at different distances from the layer of thermoelectric material 1 so that the entire temperature jump ΔT takes place within the layer of thermoelectric material 1, between its two opposite sides H and C. However, in actual fact, the real temperature diagram is the one designated by Tr. As may be seen, in actual fact, the temperature jump that occurs through the layer of thermoelectric material 1 is very small, the majority of the variation of temperature taking place in fact through the laminar layer L of each of the two flows of fluid.
FIG. 2 of the annexed plate of drawings shows, instead, how, in the case of a thermoelectric generator with solid-solid interface, the situation is close to the ideal one. With reference to FIG. 2, the reference number 1 designates once again the layer of thermoelectric material, whilst the reference numbers 2 and 3 designate two layers of material with high thermal conductivity, which are at two different temperatures. Also in FIG. 2, the diagram designated by Ti indicates the ideal variation of temperature corresponding to the optimal exploitation of the layer of thermoelectric material. As has been said, in the above ideal situations, the entire temperature jump ΔT between the two layers 2, 3 occurs within the layer of thermoelectric material 1. The diagram designated by Tr in FIG. 2 regards the real situation. As may be seen, the temperature jump that occurs through the thermoelectric layer is not exactly identical to the difference in temperature existing between the two layers 2, 3 but is almost equal thereto, the variation of temperature that occurs through each of the layers 2, 3 being in fact extremely small.